Method for cleaning aluminum and aluminum alloys

ABSTRACT

An aqueous alkaline cleaner for aluminum has a pH in the range from 10.0-12.0 and contains: 
     (A) from 0.5 to 10.0 g/L of an alkali builder component; 
     (B) from 0.5 to 10.0 g/L of aminoalkyl- and/or hydroxyalkyldi-phosphonic acids and/or their water soluble salts; 
     (C) from 0.1 to 3.0 g/L of an aluminum ion sequestering agent component; and 
     (D) from 0.5 to 5.0 g/L of a surfactant component. 
     Cleaning aluminum and aluminum alloy with such a cleaner generates an excellent surface condition with respect to de-smutting performance, water wettability, avoidance of black smut production, blackening, and paint adherence at least as good as that achieved with conventional acid cleaners, without requiring any acid wash.

TECHNICAL FIELD

The present invention relates to a novel method for cleaning aluminumand aluminum alloys (both being denoted briefly below, unless thecontext requires otherwise, by the simple term "aluminum") whichgenerates a surface condition that is optimal for subsequent conversiontreatments and that strongly resists the development of black smut onthe aluminum surface. The invention may be employed to clean the surfaceof aluminum sheet, strip, container, or the like.

BACKGROUND ART

Aluminum containers are typically manufactured by a drawing and formingoperation known as draw-ironing or drawing and ironing. This processresults in the deposition of lubricant and forming oil on the containersurface. In addition, small fragments of leftover aluminum are oftendeposited on the surface and are present in relatively large quantitieson the interior surface of the container. The container surface iscleaned prior to, for example, conversion treatment or painting of thecontainer, and the surface must be free of contaminants which wouldresult in less than an excellent water wettability and thus impairsubsequent container processing.

At present, the compositions normally employed commercially to cleanaluminum containers are aqueous sulfuric acid solutions containinghydrofluoric acid and at least one surfactant or aqueous solutionscontaining phosphoric acid, nitric acid, or Fe³⁺, and sulfuric acid andat least one surfactant. These cleaning solutions are extremelyeffective and offer many advantages, but they nevertheless suffer fromcertain types of problems inherent to such acidic cleaning compositions.Thus, for example, these compositions can dissolve and corrode thestainless steel equipment or other ferrous alloy equipment which istypically used for a container cleaning line. Moreover, discharge of anyhydrofluoric acid and fluoride present in the rinse water and spentcleaning bath causes environmental problems. In the case of Fe³⁺-containing cleaning solutions, the iron hydroxide present in thepreliminary hot water rinse prior to the cleaning step may stick in theheat exchanger.

Alkaline cleaning solutions have already been formulated in an attemptto solve these problems; however, known alkaline cleaning solutions arethemselves associated with problems which impair their commercialapplication. For example, when the use of an alkali metal hydroxidecontaining cleaning solution is attempted, an irregular etch is oftenobtained with broad range of aluminum containers. Also, when the line isinterrupted due to operational problems downstream from the containercleaning line while the spray alone continues to operate, black smut isproduced from aluminum alloy components due to excessive etching. Suchcontainers are commercially useless. In addition, the hydroxide layercontinues to grow on the surface of the aluminum after an alkalinecleaning and becomes substantially thicker than the hydroxide layerafter an acidic cleaning. A thick hydroxide layer creates problems inany subsequent conversion treatment and accordingly results in a poorcorrosion resistance. Finally, magnesium is segregated to the aluminumsurface after an alkaline cleaning of alloys that include magnesium, andthis causes, inter alia, an unsatisfactory paint adherence.

Thus, in order to remove this hydroxide layer and segregated Mg, itbecomes necessary to implement an acidic wash, for example by nitricacid, after an alkaline cleaning. However, plant space and availableequipment considerations make it difficult to introduce an acid washstep into the container cleaning line. In sum, prior alkaline cleaningsolutions exhibit various problems as detailed above.

DESCRIPTION OF THE INVENTION Problem to Be Solved by the Invention

The present invention has as its major object the introduction of amethod for cleaning aluminum and aluminum alloy which exhibits a uniformetching performance that is not subject to large changes in rate withcontinued use, provides excellent de-smutting, and, without using anacid wash, nevertheless suppresses hydroxide layer growth and eliminatessurface segregated magnesium.

SUMMARY OF THE INVENTION

As a concrete means for solving the problems associated with the priorart as discussed above, the present invention comprises a method forcleaning aluminum and aluminum alloys wherein said method ischaracterized by contacting the surface of aluminum, preferably by sprayor immersion for from 20 to 60 seconds, with an aqueous alkalinecleaning composition, preferably at a temperature in the range from 50°to 70° C., which has a pH of 10.0 to 12.0 and which comprises,preferably consists essentially of, or more preferably consists of,water and:

(A) from 0.5 to 10.0 grams per liter (hereinafter "g/L") of at least onealkali builder selected from the group consisting of alkali metalhydroxides, inorganic alkali metal phosphates, and/or alkali metalcarbonates;

(B) from 0.5 to 10.0 g/L of at least one compound selected from theaminoalkylphosphonic acids and hydroxyalkyldiphosphonic acids and/ortheir water soluble salts;

(C) from 0.1 to 3.0 g/L of at least one aluminum ion sequestering agentselected from the alkali metal gluconates, alkali metal heptogluconates,alkali metal oxalates, alkali metal tartrates, and/or sorbitol; and

(D) from 0.5 to 5.0 g/L of a surfactant component.

This cleaning method not only evidences a highly uniform etching rateand effect on the aluminum surface, but also a very robust (=durable)etching performance and excellent de-smutting performance. Moreover,growth of the hydroxide layer is prevented and the surface segregated Mgis eliminated. It therefore solves the numerous problems associated withthe prior art examples.

DETAILS OF PREFERRED EMBODIMENTS OF THE INVENTION

The alkali metal salt comprising the alkali builder preferably consistsof one or more selections from the potassium and sodium hydroxides,carbonates, and inorganic phosphates, and examples in this regard aresodium hydroxide, sodium carbonate, trisodium phosphate, and potassiumhydroxide. The quantity required for etching is 0.5 to 10.0 g/L andpreferably 1.0 to 5.0 g/L. At less than 0.5 g/L, etching becomesunsatisfactory and the aluminum surface becomes nonuniform. Noadditional effect in terms of etching capacity is observed for values inexcess of 10.0 g/L, while the aluminum surface is roughened by excessiveetching.

The aminoalkylphosphonic acid is exemplified byaminotrimethylenephosphonic acid, which has the chemical formula:##STR1## and by ethylenediaminetetramethylenephosphonic acid, which hasthe chemical formula: ##STR2## and the hydroxyalkyldiphosphonic acid isexemplified by 1-hydroxyethylidene-1,1-diphosphonic acid, which has thechemical formula: ##STR3##

The total concentration of phosphonic acids and/or their salts shouldpreferably be in the range from 0.5 to 10.0 g/L and more preferably isin the range from 2.0 to 7.0 g/L. Satisfactory inhibition of black smutproduction will not usually be achieved with less than 0.5 g/L. Noadditional significant technical benefit is observed for quantities inexcess of 10.0 g/L, and higher concentrations normally should be avoideddue to the high costs involved.

No particular restriction is placed on the surfactant in terms ofwhether it is a cationic surfactant, anionic surfactant, nonionicsurfactant, or a mixture of two or more of these types. Nonionicsurfactants are exemplified by hydrocarbon derivatives, abietic acidderivatives, ethoxylated primary alcohols, and modified polyethoxylatedalcohols. In any case, at least one surfactant selection must bepresent, and the total concentration of surfactants should be 0.5 to 5.0g/L and preferably 0.5 to 2.5 g/L.

The aluminum sequestering agent may be alkali metal gluconates, alkalimetal heptogluconates, alkali metal oxalates, alkali metal tartrates,and/or sorbitol. At least one compound is selected therefrom withoutrestriction and is added to the cleaning bath to serve as an aluminumsequestering agent. The aluminum sequestering agent should be present ata concentration of from 0.1 to 3.0 g/L. At concentrations less than 0.1g/L, bonding with aluminum ion eluting from the aluminum surface duringits cleaning will be weak and the sequestering effect will therefore beweak. The etching performance and smut removal are then readily impairedby the aluminum ion accumulating in the cleaning bath. In contrast tothis, the sequestering activity is saturated at concentrations greaterthan 3.0 g/L and an increase in effect cannot be expected.

The pH of the cleaning bath should be in the range from 10.0 to 12.0. Atvalues less than 10.0, the aluminum surface will usually be nonuniformdue to an inadequate etch, and the smut adhering to the aluminum cannotbe removed to a satisfactory degree. At pH values in excess of 12.0, thecorrosion resistance (blackening) after conversion treatment will bereduced due to the production of trace amounts of black smut as a resultof an excessive etch.

The benefits from the present invention will be explained moreconcretely below through several illustrative and comparison examples.

EXAMPLES 1 -7 (1) Cleaning Bath Compositions

The composition of the cleaning bath for each example is reported inTable 1, where the surfactants used are identified by numbers with thefollowing meaning (EO=ethylene oxide; PO=propylene oxide):

surfactant (1): {nonylphenol+11 moles EO} adduct (hydrocarbon derivativetype)

surfactant (2): {higher alcohol+5 moles EO+10 moles PO} adduct(hydrocarbon derivative type)

surfactant (3): {nonylphenol+18 moles EO} adduct (hydrocarbon derivativetype)

surfactant (4): {higher alcohol+5 moles EO+15 moles PO} adduct(hydrocarbon derivative type)

(2) Test Material

Uncleaned drawn and ironed cylindrical containers 66 millimeters(hereinafter "mm") in diameter×124 mm high, made from type A3004aluminum alloy sheet.

(3) Test Conditions

The bath temperature, treatment method, and treatment time are reportedin Table 2 for each example. Cleaning of each sample container wasconducted according to one of the following process sequences (1) and(2) in the examples, depending on the test to be performed as specifiedbelow.

Process Sequence (1):

1. cleaning

2. tap water rinse (10 seconds, spray)

3. rinse with deionized water (10 seconds, spray)

4. drying (hot air, 180° C.)

Process Sequence (2):

1. cleaning

2. water rinse (10 seconds, spray)

3. conversion treatment as follows:

agent: ALODINE™ 404 from Nihon Parkerizing Co., Ltd.

                                      TABLE 1                                     __________________________________________________________________________    Composition of cleaning baths for aluminum and aluminum alloy                        alkali               Al sequestering                                                                       surfactant                                number metal salt                                                                         organophosphonic acid                                                                         agent   (alkaline cleaning solution)                                                               bath pH                      __________________________________________________________________________    Examples                                                                      1      NaOH ethylenediaminetetramethylene-                                                                Na heptoglu-                                                                          1: 1.0 g/L   11.0                                1.7 g/L                                                                            phosphonic acid, 2.0 g/L                                                                      conate, 1.0 g/L                                                                       2: 1.0 g/L                                2      NaOH 1-hydroxyethylidene-                                                                          Na gluconate,                                                                         3: 1.0 g/L   11.5                                1.7 g/L                                                                            1,1-diphosphonic acid, 2.0 g/L                                                                2.0 g/L 4: 1.0 g/L                                3      Na.sub.3 PO.sub.4                                                                  ethylenediaminetetramethylene-                                                                Na gluconate,                                                                         1: 1.5 g/L   10.5                                5.0 g/L                                                                            phosphonic acid, 1.3 g/L                                                                      1.0 g/L 2: 0.5 g/L                                4      KOH  ethylenediaminetetramethylene-                                                                Na heptoglu-                                                                          3: 0.3 g/L   10.0                                5.0 g/L                                                                            phosphonic acid, 7.6 g/L                                                                      conate, 2.0 g/L                                                                       4: 0.5 g/L                                5      Na.sub.2 CO.sub.3                                                                  aminotrimethylenephosphonic                                                                   Na heptoglu-                                                                          1: 2.0 g/L   10.5                                10 g/L                                                                             acid, 2.0 g/L   conate, 3.0 g/L                                                                       4: 2.5 g/L                                6      NaOH ethylenediaminetetramethylene-                                                                Na heptoglu-                                                                          2: 0.5 g/L   11.0                                5.0 g/L                                                                            phosphonic acid, 7.6 g/L                                                                      conate, 0.3 g/L                                                                       3: 1.5 g/L                                7      NaOH 1-hydroxy ethylidene-                                                                         potassium                                                                             1: 2.0 g/L   10.5                                0.7 g/L                                                                            1,1-diphosphonic acid, 0.7 g/L                                                                oxalate, 1.0 g/L                                  Comparison                                                                    Examples                                                                      1      NaOH --              --      1: 2.0 g/L   12.0                                1.7 g/L                                                                2      NaOH ethylenediaminetetramethylene-                                                                --      1: 1.0 g/L   12.4                                5.0 g/L                                                                            phosphonic acid, 0.05 g/L                                                                             2: 1.0 g/L                                3      Na.sub.3 PO.sub.4                                                                  --              Na heptoglu-                                                                          3: 1.0 g/L   11.3                                3.0 g/L              conate, 1.0 g/L                                                                       4: 1.0 g/L                                4      KOH  1-hydroxyethylidene-                                                                          Na tartrate,                                                                          3: 1.5 g/L   2.4                                 0.05 g/L                                                                           1,1-diphosphonic acid, 2.0 g/L                                                                1.0 g/L 4: 0.5 g/L                                5      NaOH        1.7 g/L                                                                              5% nitric acid                                                                          1: 1.0 g/L   --                                  sodium heptogluconate                                                                     1.0 g/L          2: 1.0 g/L                                __________________________________________________________________________

                  TABLE 2                                                         ______________________________________                                        Cleaning conditions and results                                               ______________________________________                                               treatment conditions                                                            bath temperature         time                                        number   °C.    method     (seconds)*                                  ______________________________________                                        Examples                                                                      1        60            spray      50                                          2        60            spray      50                                          3        60            spray      50                                          4        60            spray      30                                          5        60            spray      20                                          6        50            spray      50                                          7        70            immersion  60                                          Comparison                                                                    Examples                                                                      1        60            spray      50                                          2        70            spray      50                                          3        60            spray      50                                          4        60            spray      50                                          ______________________________________                                               results                                                                         de-     water   black          paint                                          smut-   wet-    smut    blacken-                                                                             ad-                                   number   ting    tability                                                                              production                                                                            ing    herence                               ______________________________________                                        Examples                                                                      1        5       100     10      10     10                                    2        5       100     10      9      10                                    3        5       100     10      10     10                                    4        5       100     10      10     10                                    5        5       100     10      9      10                                    6        5       100     10      10     10                                    7        5       100     10      9       9                                    Comparison                                                                    Examples                                                                      1        5       100      1      1       3                                    2        5       100      5      5       6                                    3        5       100      1      1       5                                    4        2       100      8      7       4                                    5        5       100     10      10     10                                    ______________________________________                                         *This time was always 10 minutes in the evaluation of black smut              production in the Examples and Comparison Examples.                      

concentration: 2%

temperature: 32° C.

pH: 3.0

time: 30 seconds

method: spray

4. tap water rinse (10 seconds, spray)

5. rinse with de-ionized water (10 seconds, spray)

6. drying (hot air, 180° C.)

(4) Property Testing and Evaluation

De-smutting:

After the drying step 4 in process sequence (1), the same cellophanetape was applied and peeled off at three locations on the interior wallof the container, and the smut adhering on the tape was visuallyevaluated and scored on a 5-point scale: ##STR4## Water wettability:

After the water rinse step 2 in process sequence (1), the container wasallowed to stand for 30 seconds and the water-wetted area was thenevaluated in %.

Black smut:

The cleaning step 1 in process sequence (1) was carried out for 10minutes. After the drying step 4. in process sequence (1), the adherenceof black smut product on the container was visually evaluated and ratedon the following scale. ##STR5## Blackening:

After the drying step 6 in process sequence (2), the bottom of thecontainer was immersed for 30 minutes in boiling tap water, and thedegree of blackening was then visually evaluated and reported on thefollowing scale. ##STR6## Paint adherence:

After the drying step 6 in process sequence (2), an epoxy-urea paintsystem (film thickness=5 micrometers) was applied to the container,followed by baking for 3 minutes at 215° C. A grid pattern was then cutinto the interior surface of the container and the container wassubsequently immersed for 60 minutes in boiling test solution (testsolution=sodium chloride 5 g/L and citric acid 5 g/L, in de-ionizedwater). This was followed by a water rinse, spontaneous drying, andpeeling with tape, and the degree of peeling was visually evaluated andreported on the following scale. ##STR7##

COMPARISON EXAMPLES 1 TO 4

As for the Examples, the composition of the cleaning bath is reported inTable 1, and the bath temperature, treatment method, and time arereported in Table 2. The test material was the same as in the Examples.The treatment processes and property testing and evaluation were alsothe same as in the Examples.

COMPARISON EXAMPLE 5

The cleaning bath composition used in this Comparison Example 5 isreported in Table 1, and the test material was the same as in theExamples. However, in contrast to the Examples and Comparison Examples1-3, an acid cleaning was used for this example. The cleaning processsequence (3) was as shown below. The water wettability was testedimmediately after water rinse step 4 in the following sequence, and theblack smut production and desmutting were evaluated on samples that wereremoved from the process sequence after step 4 and then dried.Blackening and adherence were evaluated after step 8 in process sequence(3).

Process Sequence (3)

1. cleaning (60° C., spray, 50 seconds)

2. water rinse (10 seconds, spray)

3. acid rinse (40° C., spray, 30 seconds)

4. tap water rinse (10 seconds, spray)

5. conversion treatment (as in the Examples)

6. tap water rinse (10 seconds, spray)

7. de-ionized water rinse (10 seconds, spray)

8. drying (180° C., hot air)

Benefits of the Invention

The method of the present invention for cleaning aluminum and aluminumalloy generates an excellent surface condition in all respects tested(de-smutting performance, water wettability, black smut production,blackening, paint adherence) without requiring any acid wash.

The invention claimed is:
 1. A method for cleaning aluminum by contacting the surface of the aluminum with an aqueous alkaline cleaning composition that has a pH of 10.0 to 12.0 and consists essentially of water and:(A) from 0.5 to 10.0 g/L of an alkali builder component selected from the group consisting of alkali metal hydroxides, inorganic alkali metal phosphates, alkali metal carbonates, and mixtures thereof; (B) from 0.5 to 10.0 g/L of a component selected from the group consisting of aminoalkylphosphonic acids, hydroxyalkyldiphosphonic acids, water soluble salts thereof, and mixtures of any two or more of these; (C) from 0.1 to 3.0 g/L of an aluminum ion sequestering agent component selected from the group consisting of alkali metal gluconates, alkali metal heptogluconates, alkali metal oxalates, alkali metal tartrates, sorbitol, and mixtures thereof; and (D) from 0.5 to 5.0 g/L of a surfactant component.
 2. A method according to claim 1, wherein the concentration of component (A) is in the range from 1.0-5.0 g/L.
 3. A method according to claim 2, wherein the concentration of component (B) is in the range from 2.0 to 7.0 g/L.
 4. A method according to claim 3, wherein the concentration of component (D) is in the range from 0.5-2.5 g/L.
 5. A method according to claim 4, wherein the aqueous alkaline cleaning composition is contacted with the aluminum surface to be cleaned at a temperature in the range from 50°-70° C. by spray or immersion for a time of from 20 to 60 seconds.
 6. A method according to claim 5, wherein component (B) consists of ethylenediaminetetramethylenephosphonic acid, one of its water soluble salts, or mixtures thereof.
 7. A method according to claim 5, wherein component (B) consists of 1-hydroxyethylidene-1,1-diphosphonic acid, one of its water soluble salts, or mixtures thereof.
 8. A method according to claim 5 wherein component (B) consists of aminotrimethylenephosphonic acid, one of its water soluble salts, or mixtures thereof.
 9. A method according to claim 2, wherein the concentration of component (D) is in the range from 0.5-2.5 g/L.
 10. A method according to claim 9, wherein the aqueous alkaline cleaning composition is contacted with the aluminum surface to be cleaned at a temperature in the range from 50°-70° C. by spray or immersion for a time of from 20 to 60 seconds.
 11. A method according to claim 10, wherein component (B) consists of ethylenediaminetetramethylenephosphonic acid, one of its water soluble salts, or mixtures thereof.
 12. A method according to claim 10, wherein component (B) consists of 1-hydroxyethylidene-1,1-diphosphonic acid, one of its water soluble salts, or mixtures thereof.
 13. A method according to claim 10, wherein component (B) consists of aminotrimethylenephosphonic acid, one of its water soluble salts, or mixtures thereof.
 14. A method according to claim 1, wherein the concentration of component (B) is in the range from 2.0 to 7.0 g/L.
 15. A method according to claim 14, wherein the concentration of component (D ) is in the range from 0.5 -2.5 g/L.
 16. A method according to claim 15, wherein the aqueous alkaline cleaning composition is contacted with the aluminum surface to be cleaned at a temperature in the range from 50°-70° C. by spray or immersion for a time of from 20 to 60 seconds.
 17. A method according to claim 16, wherein component (B) consists of ethylenediaminetetramethylenephosphonic acid, one of its water soluble salts, or mixtures thereof.
 18. A method according to claim 16, wherein component (B) consists of 1-hydroxyethylidene-1,1-diphosphonic acid, one of its water soluble salts, or mixtures thereof.
 19. A method according to claim 16, wherein component (B) consists of aminotrimethylenephosphonic acid, one of its water soluble salts, or mixtures thereof.
 20. A method according to claim 1, wherein the concentration of component (D) is in the range from 0.5-2.5 g/L. 